Ethylene cyclic olefin polymers would be excellent rubbery materials with beneficial optical properties of a high refractive index and mechanical properties of low tension set if they had elastomeric properties. However, as is known, such polymers generally exhibit glass transition temperatures (T.sub.g) well above the generally recognized T.sub.g of elastomers (elastomers having a T.sub.g generally below room temperature, preferably below -35.degree. C.). This behavior, while generally applicable, is specifically applicable to such ethylene cyclic olefin polymers with molecular weights (number average, M.sub.n) at least five times greater than the entanglement molecular weight (M.sub.e) for such polymers.
The introduction of cyclic olefins, and in particular, fused ring cyclic olefins (FRCO) into SBCCP leads to rapid increase in the glass transition temperature (T.sub.g) of the SBCCP. These changes arise both from the introduction of catenated chains of the carbon atoms pendant on the saturated polyolefin backbone as well as from the introduction of rigidity of the fused ring cyclic olefin structure arising from the FRCO. Both of these effects have been studied and documented. In general, for the effect on the T.sub.g, the introduction of equal mole fractions of alpha olefins, cyclic olefins, and FRCO of approximately equal number of carbon atoms increases with the degree of cyclic structures introduced into the SBCCP. For example in the book "Prediction of Polymer Properties" by J Bicerno published by Marcel Dekker Inc., New York, N.Y., (1993) page 149 and thereafter, it is shown that for saturated backbone polymers composed of carbon and hydrogen, the T.sub.g of the polymers increases with addition of carbon based radical chains to the main saturated backbone of polymer. The increase in the T.sub.g is most evident for the introduction of cyclic groups in the polymers. This information is shown below in Table 1.
TABLE 1 ______________________________________ Glass transition temperature in degrees K for typical SBCCP Polymer T.sub.g in degrees K ______________________________________ Polyethylene 195 Polypropylene 233 Poly(5-methyl-1-hexene) 259 Poly(4-methyl-1-pentene) 302 Poly(4-cyclohexyl-1-butene) 313 Poly(vinyl cyclohexane) 363 Poly(cyclopentene) 362 Poly(bicylco(2.2.1)heptene) 603 ______________________________________
The data above pertains only to homopolymers. The data for copolymers is less easily available, but can be estimated. It is expected that the T.sub.g of copolymers of FRCO and other monomers such as ethylene is intermediate between the T.sub.g of the homopolymers of the constituent monomers. It is known that in such cases the T.sub.g of the copolymer depends on the relative amounts of the two olefins which form the copolymers. The relationship between the composition of the copolymer in terms of the composition of the two parent olefins has been investigated by T. G. Fox in Bulletin of the American Physical Society V1, p 123 (1956). This relationship shows that the T.sub.g of a copolymer of two monomers 1 and 2, present in weight fractions M1 and M2, whose homopolymers have glass transition temperature of T.sub.g1 and T.sub.g2, respectively is given by the relationship in Equation 2 ##EQU1##
In spite of this increment in the glass transition temperature of SBCCP containing FRCO there have been several attempts to use these SBCCP as elastomeric articles, particularly in vulcanizates. Thus, in U.S. Pat. No. 4,195,013, the author describes the formation and compounding with process oils and filler in a polymer similar to the SBCCP. However, the document does not disclose the lowering of the T.sub.g of SBCCP by dilution addition with specific process oils. The purported advantages, arise because of the `monomer which, when introduced in small quantity, makes it possible to increase the vitreous transition temperature of the tetrapolymer`. Thus, this document relies on the increases of the T.sub.g of the SBCCP to obtain the purported improvement. Shown in the data in Table III of the document, the T.sub.g of the polymers increases with addition of the FRCO and is likely to be causative for the purported improvements described in the document.
Moreover, the general use of process oils to lower the T.sub.g of SBCCP containing FRCO has not been suggested previously. In U.S. Pat. No. 5,290,886 and U.S. Pat. No. 5,397,832, the lowering of the T.sub.g of polyolefin elastomers and plastics by the addition of process oils has been shown. These process oils can be classified as the first class and second class (vide infra) in the specification of the current invention. In '886 and '832 the process of lowering the T.sub.g by using process oils as well as the process of selection of the process oils is discussed. However, neither of the suggested polymers contain a FRCO.
There is a need therefore for an ethylene cyclic olefin copolymer defined as an SBCCP containing a FRCO that can include elastomeric properties, particularly having a sufficiently low T.sub.g.